- [Instructor] Let's set up a host firewall
using IP tables.
The default rules for host firewalls
are blocking all the incoming or ingress packets,
allowing all the outgoing or egress packets
and then disabling forwarding.
Forwarding is for redirecting a packet coming
to a particular network interface card, or NIC,
to another NIC.
Your computer usually
has only a single network interface card.
In our case, all we care about is the host itself.
Therefore, forwarding is irrelevant.
Let's start by looking at the current Netfilter settings.
We'll start by typing sudo,
which temporarily makes you a root or super suer
only when you're issuing that particular command.
Type sudo
space iptables -L
and press Enter.
If your operating system or OS asks for a password
for the root, provide one.
The terminal displays the current Netfilter settings.
According to the output,
the chain INPUT accepts all the incoming packets.
The FORWARD chain also accepts packets.
The OUTPUT chain accepts all the outgoing
or egress packets.
Let's see if the firewall rules work.
Before moving on, let's check the IP address
of the Ubuntu host.
Type ifconfig.
Press Enter.
The IP address is 10.0.0.4.
Keep this IP address in mind
because we are going to ping this IP address
from another host.
The ping command is used
for checking if a host is up or down.
First, activate a command prompt.
Type cmd.
Choose Command Prompt.
Type ipconfig.
The IP address of this host is 10.0.0.5.
Now I'm going to be pinging the Linux host
from my Windows client
by typing ping 10.0.0.4.
Press Enter.
My pings are receiving responses
from the Ubuntu host.
Great, the firewall rules are working
because we want them to accept the incoming packets,
like my pings.
Now we're going to set up our Netfilter firewall
to block all the incoming traffic
while disabling forwarding
and allowing the outgoing traffic.
The first command to give is sudo iptables -P.
Make sure P is capital.
Dash P indicates a default rule
for a particular chain.
To block forwarding,
let's type FORWARD DROP.
Press Enter.
Let's check the updated forwarding rule.
I can recall my previous commands
by using the up arrow key
and that's what I just did.
The command is sudo iptables -L.
Press Enter.
Do you see the word DROP next to FORWARD?
It was ACCEPT when we checked the status last time.
Finally, let's drop all the incoming packets
by typing sudo iptables -P INPUT DROP.
Press Enter.
At this point, if you're connecting to your virtual machine
through a remote desktop client,
you'll lose your access.
That's exactly what happened to me here.
The drop command certainly worked.
Now let's go back to our Windows host
and try to ping the Ubuntu virtual machine again.
I can recall my previous command here
by using the up arrow key again.
The command is ping 10.0.0.4.
Press Enter.
Your ping requests are timing out.
There is no response,
which means that the firewall is doing its job.
What do you think?
Setting up the host file using the CLI
isn't that bad, right?